1. Field of the Invention
This invention relates to a metal-oxide-semiconductor field-effect transistor (MOS FET) device, and more particularly the invention relates to a MOS FET device whose output drain current varies in proportion to its control gate voltage.
2. Description of the Prior Art
In various digital circuits, MOS FET is widely used, and it is now one of the major digital circuit elements. Since MOS FET can function as an amplifier, it is also used in linear electronic circuits. For instance, it is used as an amplifying element in sensor-semiconductor assemblies such as MOS strain gauges and MOS pressure sensors, and it is also used in control linear electronic circuits such as low resistance loads and inductive loads.
A typical conventional MOS FET has a rectangular source zone and a rectangular drain zone which are disposed so as to face each other, and a gate insulating film is formed between the source zone and the drain zone so that a gate electrode formed on the insulating film extends its electrical field to a current channel between the source zone and the drain zone. The output drain current is controlled by a voltage applied to the gate electrode. Such conventional MOS FET has a shortcoming in that the output drain current varies as quadratic function of the control gate voltage, so that when the MOS FET is used as an amplifying element, its output must be converted into a linear quantity. In this case it is necessary to use a separate converter circuit for changing the output into a linear quantity.
The need of the separate converter for linearization of the output drain current tends to complicate the signal processing circuits and to increase the production cost. Another shortcoming of the conventional MOS FET is in that, when it is used as a control linear circuit element such as a low resistance load or an inductive load, the drain current is susceptible to sudden change in case of relatively minor change in power source voltage, because it increases as a quadratic function of the control gate voltage.